The Cerebellum is
a peach-sized structure situated at the base
of the brain. It is highly-folded and has been called the brain with
the brain - indeed the very name comes from the Latin for "little brain".
See this diagram:

The cerebellum is responsible
for coordinating movement, planning, motor activities, learning and remembering
of physical skills and for some cognitive abilities. Interestingly, the size
of this brain region within any mammal species is a good indicator of its
the physical capability.

The cerebellum controls
movement by collecting sensory nerve inputs, such as limb position,
balance information and vision, and synthesising them together to
control movement by sending nerve transmissions down motor nerve outputs. The
learning of physical tasks is done by trial and error and then stored into
cerebellar memory. This is the reason that we never forget certain skills
such as riding a bike. There is some evidence that mental activities are
also co-ordinated in the cerebellum which could explain why cognitive
dysfunction is sometimes associated with damage to the cerebellum.

The cerebellum is
divided into two hemispheres by the central "vermis". The surface of each
hemisphere is made up of grey matter surrounding
a large mass of white matter (nerve
cells with myelinatedaxons).
The whole structure is connected to the rest of the central
nervous system by three very broad tracts of white matter called the
cerebellar peduncles. These are the brachium pontis which connects to the pons,
the restiform body which connects to the medulla
and the brachium conjunctivum which connects to the mesencephalon.

Damage to the cerebellum
or the cerebellar peduncles is very common in multiple
sclerosis. This is not surprising given the large amount of white matter in these structures.

Some of symptoms
associated with damage to the cerebellum or the nervous tracts leading
to it are: